DETERMINATION OF CEFTIOFUR AND ITS METABOLITE DESFUROYLCEFTIOFUR IN BOVINE SERUM AND MILK BY ION-PAIRED LIQUID-CHROMATOGRAPHY

A simple and sensitive liquid chromatographic method has been develope d for the simultaneous determination of ceftiofur and its metabolite d esfuroylceftiofur in bovine serum and milk. The method involved an ult rafiltration of diluted serum/milk with an equal volume of 50% acetoni trile through a 10 000 dalton molecular mass cut-off filter. Separatio n of ceftiofur and desfuroylceftiofur from the other serum/milk compon ents was performed by ion-paired (octane and dodecanesulfonate) liquid chromatography using a reversed-phase column eluted with acetonitrile water solution. The ultraviolet visible absorbance of the column effl uent was monitored in 200-350 nm range of a photodiode-array detector or at lambda(max) 289.6 nm for ceftiofur, lambda(max) 265.8 nm for des furoylceftiofur and lambda(max) 271.4 nm for dimer of desfuroylceftiof ur. Recoveries of ceftiofur from bovine milk spiked with 1 and 10 mug/ ml were 95.9 and 97.0% with coefficients of variation of 3.69 and 2.51 %, respectively. Recovery of ceftiofur from bovine serum spiked with 1 0 mug/ml was 90.4% with a coefficient of variation of 5.29%. A correla tion coefficient of 0.9992 occurred with ceftiofur in aqueous solution s (n = 5, in duplicates). The limit of detection was estimated to be a pproximately 50 ppb (ng/ml). Additionally, this paper documents the pr esence of a ceftiofur metabolite in bovine serum under in vitro and in vivo conditions. The metabolite was identified as desfuroylceftiofur together with its dimer 3,3'-desfuroylceftiofur disulfide by thermospr ay liquid chromatography mass spectrometry.